The invention relates to a data carrier which is configured to communicate with a communication station with the aid of a carrier signal and which includes a receiving-means configuration having a switching means and having a first transmission coil that can be short-circuited and having a second transmission coil and having a capacitor configuration.
Such a data carrier is commercially available and is consequently known. The construction of the relevant part of the known data carrier is shown in FIG. 1.
The known data carrier DC includes a receiving-means configuration RC and a chip CH connected to the receiving-means configuration RC. The receiving-means configuration RC includes a switching means S, a first transmission coil L1 that can be short-circuited with the aid of the switching means S, a second transmission coil L2 arranged in series with the first transmission coil L1, and a capacitor configuration CC arranged in parallel with the series arrangement of the first transmission coil L1 and the second transmission coil L2. The capacitor configuration CC now consists of a capacitor C external to the chip CH and of the input capacitance of the chip CH, but this is shown as a single capacitor C in an equivalent diagram. The switching means S is switchable between a conductive switching state and a non-conductive switching state. The switching means S can be changed over with the aid of control means CM, which are incorporated in the chip CH and which are connected to the switching means S via a control line CL.
In a mode of communication between the data carrier DC and a communication station the switching means S is in its non-conductive switching state, as a result of which the two transmission coils L1 and L2 are arranged in series and this series arrangement of the two transmission coils L1 and L2 is arranged in parallel with the capacitor configuration CC. The two transmission coils L1 and L2 than have an inductance value and the capacitor configuration CC has a capacitance value, which inductance value and which capacitance value are selected in such a manner that the resonant circuit formed by the two transmission coils L1 and L2 and the capacitor configuration CC has a resonant frequency which corresponds to the carrier signal frequency fC of the carrier signal CS used in the communication process.
In a rest mode of the data carrier DC, when the data carrier DC is not in a mode in which it communicates with the communication station, flee switching means S is in its conductive state. When in this operating mode of the data carrier DC, i.e. in its rest mode, the data carrier DC enters into communication with a commutation station, this results in a coil current I1 through the first transmission coil L1, which is an inductive coil current having a phase lag with respect to the voltage across the first transmission coil L1. Furthermore, it results in a coil current I2 through the second transmission coil L2, i.e. a capacitive coil current having a phase lead with respect to the voltage across the second transmission coil L2. Each of these two coil currents I1 and I2 produces a magnetic field with the aid of the respective coil L1 or L2, which two magnetic fields attenuate one another, the aim being that the two magnetic fields cancel one another, so that owing to the desired cancellation of the two magnetic fields flee data carrier DC cannot have any adverse effect on the transmission coil of a nearby data carrier.
Owing to the selected design, which uses two fixed-value transmission coils L1 and L2 and a fixed-value capacitor configuration, which elements always exhibit a spread in value, it is substantially impossible with the known data carrier DC to obtain currents I1 and I2 through the two transmission coils L1 and L2 which cause magnetic fields which cancel one another. Thus, with the known data carrier DC the two transmission coils L1 and L2 always produce a residual magnetic field when the data carrier DC is in its rest mode, in which the switching means S is in tis conductive state, as a result of which the residual magnetic field exerts an undesired influence on a nearby data carrier, which undesired influence results in the resonant frequency fR no longer corresponding to the carrier signal frequency fC, as a result of which the receiving means configuration RC of the nearby data carrier DC does not guarantee a correct reception of a carrier signal CS and, consequently, the generation of energy from the received carrier signal CS is not satisfactory, which leads to a distinct reduction of the range of a nearby data carrier DC when the nearby data carrier is set to its communication state, i.e. a communication mode, in which the switching means S of the nearby data carrier is set to its non-conductive state.